(a) Field of the Invention
The present invention relates to an organic light emitting diode (“OLED”) display. More particularly, the present invention provides an OLED display and a method of manufacturing the same for improving white light emitting efficiency and simplifying a manufacturing process thereof.
(b) Description of the Related Art
Display devices using a cathode ray tube have been widely used. However, display devices using cathode ray tubes have drawbacks that the volume and weight thereof are large and heavy, respectively, and that they are not easily portable. Recently, in order to overcome the drawbacks of display devices using cathode ray tubes, liquid crystal displays and plasma display devices have been developed and used. Use of liquid crystal displays and plasma display devices have provided rapid progress in space saving and portability.
A liquid crystal display is a non-emissive device that includes a light source for emitting white light and a liquid crystal display unit for controlling the transmittance of the light emitted from the light source. The response speed of a liquid crystal display is only as fast as the time that it takes for a twisted nematic crystal to twist or untwist. Therefore, the liquid crystal display has drawbacks such as high power consumption and slow response speed. A plasma display device also has drawbacks such as high power consumption, driving complexity and low resolution. The inherent drawbacks of the plasma display come from the size of the plasma cells necessary to make an individual pixel and the nature of the injected ionizing gas which must be driven therein. In order to overcome the drawbacks of the liquid crystal display and the plasma display device, much research regarding an organic light emitting diode (“OLED”) display has been undertaken. The OLED display is itself a light-emitting device, and it may contain a plurality of light-emitting devices arranged on a substrate in a matrix and an additional substrate for protecting the substrate with the light-emitting devices. The OLED display has characteristics of low power consumption, high response speed, wide viewing angle and high resolution.
The OLED display operates on the principle that organic emission layers, which are placed between an anode providing holes and a cathode providing electrons, generate excitons by hole-electron coupling. The excitons emit light because of the energy released by the coupling (otherwise known as de-excitation). In order to display full color images, the OLED display includes a pixel array for emitting red, green and blue colors. However, the emission efficiency and lifetime of the different organic emission layers used to make red, green and blue pixels differ from each other. Therefore, various remedies have been introduced. In order to solve the described problems of the OLED, U.S. Pat. No. 6,366,025 discloses a technique for forming red, green and blue pixels each having different areas. However, the OLED display having different sized pixels has difficulties in design and driving, such as a low response time.
The OLED display may realize full color by overlapping red, green and blue emission layers having the same areas in one pixel, and disposing a color filter on the emission layers. Such a structure is disclosed in U.S. Pat. No. 6,392,340. In this case, the overlapping emission layers have the same areas and in combination emit white light. The white light is then passed through a color filter to obtain red, green and blue light. In the OLED disclosed in U.S. Pat. No. 6,392,340, the lifetime and characteristics of the emission layers also differ from each other. Also, it has difficulties in that its high luminance white light emitting lifespan is reduced because of a strong interaction between the different emission layers.